A database is a structured collection of data that is stored in a computer system. The data is typically organized according to a database model such as a relational model. Other models including the hierarchical model and the network model use a more explicit representation of relationships between objects and data. Database technology has become a pervasive and essential element of the corporate infrastructure. Corporations around the world use databases to manage everything from inventory, customers, sales, marketing, IT, human resources, business development, and many other facets of the business ecosystem.
Corporations often employ many people and have an intricate web of corporate relationships. For example, many companies are actually holding companies for other companies, or have many subsidiaries. These corporations, for example, need to be able to manage their employee records such that employee records of one company are kept separate from those of the other companies—however they also want to keep all company records in one data center for simplicity and manageability sake. One approach is to maintain multiple separate databases, one for each company, however if a corporation owns thousands of companies, managing and administering thousands of databases provides for an extremely complex and demanding task.
Separation of data belonging to separate entity domains (e.g. corporations or customers) is extremely important for companies. Only data owned by a particular company or customer should viewable by that company or customer. All other data should be implicitly invisible to non owners of that data. Thus, secure data isolation is an important requirement of any database system that contains data of more than one entity.